Meat Is Linked to Higher Cancer Risk, W.H.O. Report Finds

An international panel of experts convened by the World Health Organization concluded Monday that eating processed meat like hot dogs, ham and bacon raises the risk of colon cancer and that consuming other red meats “probably” raises the risk as well. But the increase in risk is so slight that experts said most people should not be overly worried about it.

The panel did not offer specific guidelines on red meat consumption. But its conclusions add support to recommendations made by other scientific groups like the federal government’s dietary guidelines advisory committee, which has long discouraged the consumption of red and processed meat. And the report could also influence health agencies such as the European Food and Safety Commission.

Experts not involved in the report said that the findings should give people more reason to “moderate” their intake of processed meat. But they cautioned that any increased risk of cancer was relatively small.

Nonetheless, the panel’s conclusions evoked strong responses, with significant resistance from the meat industry and from some environmental groups calling for warning labels on meat.

The report placed processed meat into its Group 1 category, which means the panel found “sufficient evidence” that it could cause cancer. While other substances in this group include alcohol, asbestos and tobacco smoke, they do not all share the same level of hazard. The risk attributed to smoking, for example, is many orders of magnitude greater than the risk associated with eating red meat, said Dr. John Ioannidis, the chairman of disease prevention at Stanford University.

“I think it’s very important that we don’t terrorize people into thinking that they should not eat any red meat at all,” said Dr. Ioannidis, who was not involved in the new report. “There’s some risk involved, but it’s much less than smoking or alcohol. I think it would be an exaggeration to say based on this that no one should be eating red or processed meat.”

Smoking causes a roughly 20-fold increase in a person’s risk of developing lung and other types of cancer, and every year it results in about a million deaths worldwide. In comparison, a person’s risk of colorectal cancer rises by a factor of about 1.1 or 1.2 for every serving of processed meat consumed per day. This means that based on the report, diets high in processed meat could be expected to contribute to about 30,000 deaths per year across the globe, though the true number could also be far less, Dr. Ioannidis said.

“There is still a lot of uncertainty,” he added.

The committee that issued the new report, the International Agency for Research on Cancer, consists of 22 public health, cancer and other experts from 10 countries. The group, which reviewed 800 studies on cancer in humans, acts as an adviser to the World Health Organization, focusing on environmental and lifestyle factors that may contribute to the disease.

Since 1971, the group has evaluated more than 900 such factors as part of its “monographs” program, assigning each factor to one of five different classification groups based on the likelihood of it playing a role in cancer.

About 120 of these factors have been characterized as carcinogenic to humans and assigned to the agency’s Group 1 category. The other groups range in classification from “probably carcinogenic,” “possibly carcinogenic,” and then “not classifiable” and finally “probably not carcinogenic.”

The factors evaluated by the group over the years include coffee, sunlight and night-shift work, and only one of these has ever been listed as “probably not” carcinogenic: a nylon manufacturing chemical found in drinking water supplies.

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Although scientific studies have linked the consumption of meat to cancer, in London, at least, people are skeptical about the findings.

The panel defined processed meat as those “transformed through salting, curing, fermentation, smoking or other processes to enhance flavor or improve preservation.” It said there was sufficient evidence based on human research — mainly large observational studies — that processed meat could be added to its Category 1 classification, along with a broad range of substances such as mineral oils, estrogen, ionizing radiation and diesel engine exhaust.

But it also cautioned that the substances were not all associated with cancer to the same extent.

“This does NOT mean that they are all equally dangerous,” the panel said in a statement, adding its own emphasis. “The I.A.R.C. classifications describe the strength of the scientific evidence about an agent being a cause of cancer, rather than assessing the level of risk.”

As for red meat — which it characterized as muscle meat such as beef, veal, pork, lamb and mutton, among others — the panel said it was “probably” carcinogenic based on “limited evidence.” It said the association was observed mainly for colorectal cancer, but that diets high in red meat were also linked to pancreatic and prostate cancer.

The risks arise from chemicals produced by processing the meats and from cooking. Cooking at high temperatures or with the meat in direct contact with a flame can produce certain types of carcinogens, but the report said there was not enough data to support conclusions about whether the way meat was cooked affected cancer risks or about whether it was better to eat it raw, which carries its own risks.

Susan Gapstur, the vice president of epidemiology for the American Cancer Society, noted that colorectal cancer was the third-most commonly diagnosed cancer among men and women in the United States, and she called the panel’s conclusions “an important step” in helping people make more healthful dietary choices. The Cancer Society’s most recent nutrition and physical activity guidelines emphasize choosing fish, poultry or beans as alternatives to processed and red meat, and for those who eat red meat, the guidelines urge them to choose lean cuts and smaller portion sizes.

But James Coughlin, a nutritional toxicologist and a consultant for the National Cattlemen’s Beef Association, said the panel’s conclusions were based on “weak associations” that did not support its overall conclusions. He pointed out that even the panel itself was divided on the issue: Of 22 members who voted on its conclusions, seven either disagreed or chose to abstain.

“That rarely ever happens,” he said. “The I.A.R.C. looks for consensus, and occasionally there’s one or two people who disagree. We’re calling this a majority opinion as opposed to a consensus or unanimous opinion.”

Christine Hauser contributed reporting.

A version of this article appears in print on , on Page A8 of the New York edition with the headline: Report Links Risk of Some Cancers to the Consumption of Processed or Red Meat. Order Reprints | Today’s Paper | Subscribe